This invention relates to a vice, particularly suitable for mounting on a machine tool bed.
Vices for holding workpieces during their mechanical machining represent a basic tool which is among the most ancient and common of a workshop, and which has undergone continuous change and development to adapt it to the increasingly strict requirements of technology. These strict requirements are evident typically for example in milling, where very high powers are attained by the use of hard metal (widia) milling tools which enable deeper and faster passes to be made, and because of the strengthening of milling machines, so much so that the weak point in the machining process, namely that which limits the machining speed, is precisely the means for holding the workpieces being machined. The requirements of a vice in such powerful machining are that it must not allow the stressed workpiece to move, must not cause it to vibrate and must not vibrate with it, and must allow the workpiece to be rapidly gripped and released.
Traditional mechanical screw vices, even of improved type, cannot apply, by manual lever operation, more than 2000 kg of closure force and this can be raised to 4000 to 5000 kg by hammer blows, with consequent tool damage and loss of time. A simple and efficient method of increasing the clamping force and satisfying the larger common requirements, which are tending towards 20,000 kg is the introduction of the known principle of the hydraulic press with manual operation, this latter being an advantage as an operator must in all cases be present. This is applied in the following manner: using the usual handle, a mobile vice block is moved forward by means of a screw or generally by motion transmission means. When the block is halted by the workpiece, the handle continues to rotate to screwfeed a piston floating in a hydraulic sump, said piston pushing a secondary larger piston rigid with the mobile jaw, so passing to a second stage which may be called "force transmission." This force multiplication, of the order of ten times, requires a like multiplication in the stroke of the piston thrust by the handle, and thus a greater time. The biggest disadvantage of this method however is its relative mechanical complication, which has already been described. In order to speed up the movement and lighten the work of the operator, hydraulic operation of the vice has been conceived.
This method satisfies all the requirements of proper continuous clamping, but presents other constructional and operational disadvantages. As workpieces of very different sizes have to be clamped, the dynamic piston must have a considerable stroke, and a rod which projects by at least the same length. This fact leads to stability problems which are solved by very costly constructions. Moreover, the long idle movements are too slow. It was then decided to combine the mechanical worm device with the hydraulic device, to obtain the advantages of the two types and avoid the disadvantages peculiar to one or the other, particularly, the jaw setting movements are of the screw type, while the workpiece is clamped under pressure between the jaws hydraulically. This combination, which is today the most widespread of high power vices, has been effected in various ways. According to the example of the vice with the hydraulic press, from which when in position the actual mobile jaw projects.
This system requires two extra guides to move the jaw relative to the carriage. To avoid these supplementary guides, which are in themselves delicate members, a second type uses the same guides for the jaw and for the carriage with drived worm, but because of space requirements the jaw slide, in the form of a second carriage, has to be made too short and therefore insufficiently guided for the requirements of its operation and the stresses to which it is subjected. In a third type, the difficulty has been overcome by making both jaws mobile, one for large movements and screw operated, and one for small clamping movements operated hydraulically. But although this method overcomes the space problem, it aggravates the cost problem as it removes the advantage of the fixed jaw. It is easily apparent that holding a jaw on guides requires gibs of much larger dimensions and precision than holding a simple positioning and thrust bearing carriage, which does not require precision.
In a fourth type, the strokes of the screw and piston are reduced by arranging, on the bed comprising the guides, holes for example at three equal distances apart to enable the carriage, with the jaw projecting therefrom or forming an extension of it, to be moved manually and fixed by keys to the bed.
A fifth type of combined operation vice of the known art is different from the previous ones in that it lacks screw operation, which is replaced, only for the purpose of halting the carriage, by a fixed sawtooth toothing on the guide surface and an opposing mibile sawtooth toothing engaging therewith, on the carriage. The carriage is here positioned by hand by articulatedly raising the carriage, or at least the toothing associated therewith, and then engaging the two toothings in the required position. As the teeth of these latter are opposed, they prevent withdrawal of the jaws, and the carriage remains fixed and allows the relative jaw to emerge by hydraulic action for clamping purposes. The disadvantages of this original method are the manual movement and the discontinuous positioning of the carriage with the jaw, governed by the pitch of the teeth.
The five listed types represent substantially all the methods proposed by the known art.